FIG. 1 is a cross sectional view showing an example of a conventional light-triggered thyristor.
In FIG. 1, (1) denotes an element of a light-triggered thyristor having a light-triggered photosensitive portion (1a) formed in a first major surface thereof, the photosensitive portion (1a) being a triggered portion, (2) denotes a reinforcing metal disc made of a metal material having a coefficient of thermal expansion approximate to that of the element (1), a second major surface of the element (1) being fixed to the reinforcing metal disc. (3) denotes a first electrode member which is made to be pressured and contacted to an electrode formed so as to surround the photosensitive portion (1a) in the first major surface of the element (1), (4) denotes a second electrode member pressured and contacted to the reinforcing metal disc (2), (5) denotes an insulating cylinder made of alumina ceramics and the like and being provided so as to surround the element (1), the reinforcing metal disc (2) and both electrode members (3) and (4), (6) denotes a first flange made of a ring-like metal plate and being fixed, in a gas-tight manner, to a first end surface of the insulating cylinder (5) and having an inner peripheral surface fixed in a gas-tight manner to the outer peripheral surface of the first electrode member (3), (7) denotes a second flange being fixed in a gas-tight manner to a second end surface of the insulating cylinder (5) and having an inner peripheral surface fixed in a gas-tight manner to an outer peripheral surface of the second electrode member (4), just like the first flange (6), (8) denotes a lateral groove being formed in an end surface of the first electrode member (3) opposed to the element (1) so as to extend internally radially from the outer peripheral surface thereof and extend beyond a portion corresponding to the photosensitive portion (1a), the width of the lateral groove being larger than the dimension of the photosensitive portion (1a), (9) denotes a through-hole provided in a portion of the insulating cylinder (5) corresponding to the lateral groove (7), and (10) denotes a light guide made of a glass bar member having a large transmittance and having a first end portion adjacent to the photosensitive portion (1a) and a second end portion leading to an exterior of the insulating cylinder (5) through the lateral groove (8) and the through-hole (9) so that an outer peripheral surface of the second end portion is sealed in a gas-tight manner to an inner wall surface of the through-hole (9), the light guide (10) being a guide for a trigger signal for guiding a triggering light signal from the exterior to the photosensitive portion (1a).
Now, an assembling procedure of such conventional example will be described.
First, an insulating cylinder (5) is prepared which inner peripheral surface is ground precisely using a grinding wheel of diamond and the like, so that the inner diameter thereof is slightly larger than the outer diameter of the reinforcing metal disc (2) in order to arrange the reinforcing metal disc (2) therein, and then the first electrode member (3) is inserted from the first end surface side of the insulating cylinder (5) into the interior thereof so that the first electrode member (3) is fixed in a gas-tight manner, to the first end surface of the insulating cylinder (5) by using the first flange (6).
Then, with the tip of the first end portion of the light guide (10) not exceeding the level of the end surface of the first electrode member (3) and being precisely positioned in an axial center of the insulating cylinder (5), the outer peripheral surface of the second end portion of the light guide (10) is fixed in a gas-tight manner to the inner wall surface of the through-hole (9). Subsequently, the photosensitive portion (1a) of the element (1) and a center portion of the reinforcing metal disc (2) are made to coincide with each other so that the element (1) is fixed onto the surface of the reinforcing metal plate (2). Then, the reinforcing metal disc (2) having the element (1) fixed thereto is rested on the end surface of the second electrode member (4) so that the reinforcing metal disc (2) contacts with the end surface. The rested body is inserted from the second end surface of the insulating cylinder (5) into the interior thereof, so that the element (1) is made to contact with the end surface of the first electrode member (3) and the second electrode member (4) is fixed in a gas-tight manner to the second end surface of the insulating cylinder (5) by using the second flange (7). Thus, such conventional assembling operation is completed.
On the other hand, in such a conventional example, there are some possibilities that a slight deviation or offset between the tip of the light guide (10) and the photosensitive portion (1a) may occur, since it is extremely difficult to seal the outer peripheral surface of the second end portion of the light guide (10) to the inner wall surface of the through-hole (9), with the tip of the first end portion of the light guide (10) being precisely positioned in an axial center of the insulating cylinder (5) and also it is extremely difficult to fix the element (1) to the major surface of the reinforcing metal disc (2) with the photosensitive portion (1a) of the element (1) being registered with the center of the reinforcing metal disc (2). In case where such deviation or offset occurs, the amount of transmission of a light signal from the tip of the light guide (10) to the photosensitive portion (1a) decreases and a light triggered sensitivity becomes worse and hence there is a fluctuation of the light-triggered sensitivity. In addition, it takes much time to grind precisely an inner peripheral surface of the insulating cylinder (5) made of alumina ceramics and the like, which makes a manufacturing cost higher.